Why is it that, nine times out of ten, the 'mysterious girl' just ain't that mysterious?

Surely it must be possible to make an OC or group of OCs look suitably dark and mysterious without insulting your readers' intelligence and making the canon cast look, in return - if you'll pardon the expression - like a group of complete idiots?

Yup, it's the good old Idiot Plot again, as applied to hideously lame fanfiction about mysterious girls crashing the lives of a group of characters who always got by just fine without them. I've come across this particular fanfiction meme in all manner of OC fics, both good, bad and ugly - well, okay, so it's mainly just the bad and the ugly and the OCs in question are normally screaming Sues. But they're screaming Sues with secret identities... which wouldn't by rights stay secret for more than about five seconds, if only the regulars had more than half a cupful of brain between them.

What's that? You say the regular characters of Insert Fandom Here do have more than half a cupful of brain between them? Well, golly gee. Now if only someone would tell the Suethors that.

We've all seen it especially if we happen to be in the Weiss Kreuz fandom. A pretty girl or group of girls the regulars have never heard of shows up completely at random for... some amazing reason... okay, plot contrivance. Usually, said girl will have some utterly unmistakeable physical feature the canon characters couldn't help picking up on almost immediately, like bright red eyes, or white hair, or she's an American in a country where 0.6% of the population are foreign (and most of them are Korean). And, all of a sudden, there are mysterious girls going round kicking ass or stealing stuff or constantly saving them from bad guys when they never had any trouble looking after themselves before, and generally getting in the way. At the very least they're outclassing them at every possible opportunity.

And they have bright red eyes or white hair or are, you know, American.

And for some reason the regulars are utterly incapable of working out who this mysterious woman might be. How many red-eyed, white-haired American girls can there be in Japan?

( But It Gets Stupider... )

Seriously, fanthings. Codenames that would have the average eight year old rolling their eyes, they're so painfully easy to decipher, and references to physical features you the ficcer have already beaten your readers over the head with do not add up to Who Is That Mysterious Girl. There's no point in going on about dark figures and shadowy features when it's so blatantly, screamingly obvious that the beautiful young girl the regulars conveniently bumped into is the mysterious woman they're now supposed to be facing off against: there'd be absolutely no reason for the new character to be in the story otherwise.

If you want to keep your Sues' identities a secret don't give us, and the regulars, chapter and verse on their lives. Simple.